Since a planar multi-electrode array was proposed to study the transmission mechanism of neural signals in 1972, microelectrode arrays have been extensively used in the biomedical engineering. The brain or a neural network is a complicated network consisting of many neurons interconnecting each other. Understanding the operation of the neural network is very important to diagnose or treat neural diseases or fabricate neural prostheses. A probe can easily puncture the skin to detect the electrophysiological signals in vivo. A probe may also function as an intermediary between analog physiological signals and digital signal analysis.
FIG. 1 shows a microelectrode array 10 for detecting neural signals. The microelectrode array 10 comprises a base 11 and a plurality of probes 12 connected to the base 11. Each probe 12 has a plurality of electrodes 13. For example, each probe 12 has four electrodes 13 in FIG. 1. Each electrode 13 is electrically connected to a metal pad 15 of the base 11 via a wire 14. Each wire 14 is insulated from the environment. The neural signals detected by the electrode 13 is transmitted to the base 11 via the wire 14 and then processed by the succeeding devices.
Carbon nanotube, which was found by S. Iijima in 1991, has a superior electric conductivity because of its special structure. Thus, carbon nanotube has been widely used in the nanometric electronic elements. The electrode interfaces of the conventional probes are usually made of a metal having better biocompatibility, such as gold, platinum, titanium, or platinum black. However, the interfacial resistance of the metal electrode increases when the size of a metal electrode is reduced to a very small scale. Thus, the efficiency of the entire circuit decreases.
Carbon nanotube has very large surface area, high electrical conductivity, better physicochemical properties, better chemical inertness and better biocompatibility. Therefore, more and more applications use carbon nanotube as the interface of neural electrodes, for example, “Carbon Nanotubes for Neural Interfaces” by David Ricci; “Carbon Nanotube Coating Improves Neuronal Recording” by Edward, et al., Nature Nanotech., 2008; “Neural Stimulation with a Carbon Nanotube Microelectrode Array” by Ke Wang, Nano Lett., 2006; “Carbon Nanotube Substrates Boost Neuronal Electrical Signaling” by Viviana Lovat, et al., Nano Lett., 2005; “Carbon Nanotube Micro-Electrodes for Neuronal Interfacing” by E. Ben-Jacob, et al., J. Mater. Chem., 2008.
The abovementioned technologies are only the rudimentary carbon nanotube applications in the neural electrode interface. The present invention further modifies the carbon nanotube electrode interface and forms the functional groups, which neuron cells prefer to adhere to. Therefore, neural signals were enhanced with the use of this modified CNT electrode.